As for a hermetically sealed container, for example, as for a beverage container, various containers such as bottles, cans, plastic containers and the like are known. In recent years, cans or plastic containers have been widely used from the viewpoint of convenience such as their good handlability and the like.
Among these, cans are being widely distributed for the reasons such as low container prices, high production rate, high transportation efficiency and the like. These cans are usually formed from a cylindrically shaped “container body” having a bottom, and a “lid” which seals the mouth portion of the container body. Since the method of adequately bonding these container body and lid, and hermetically sealing a content such as food, beverage or the like is limited, cans made from metals such aluminum, steel and the like are being distributed in the current market.
This bonding of the container body and the lid is carried out by seaming, in which the edge part of the container body are stacked with the edge part of the lid to form a flange structure, and mechanically superimposed. Since this seaming process is a process which utilizes the mechanical deformation of metallic members, the lid is generally formed from a member that is thicker than that of the container body, and is provided with a polymer material such as styrene-butadiene rubber, polyvinyl chloride or the like, for the purpose of content sealing. As such, since a polymer material is needed, and the lid is made thicker, the amount of the metallic material used is increased.
Thus, in order to solve this problem, technologies for performing the sealing of cans by laser welding, targeting metal cans, have been disclosed (see, for example, International Publication NO. WO 02/42196 A2; Japanese Laid-Open Patent Publication No. JP-A-63-194885; and Japanese Laid-Open Patent Publication No. JP-A-61-289932).
Another characteristic of metal cans involves the use of a high speed production line running on at a rate of several hundred cans to 2000 cans per minute. In conventional seaming apparatuses, a plurality of seaming heads are needed to cope with this production rate, and thus the apparatus size becomes relatively larger. As a result, until the lid is mounted on the container body filled with a liquid content in a seaming apparatus, it will be necessary in general for the container body to be conveyed over a distance of several meters on a conveyor, while being in a state that the container body is open to the external air. Due to the high conveying speed, as well as the transit of the container body between the seaming apparatus and the conveyor, the container body is subjected to external impacts, and as a result, gas exchange with the external air or liquid spillage occurs. Gas exchange accelerates deterioration of the liquid content through oxygen pickup. Particularly in the case of carbonated beverages, the carbon dioxide concentration of the liquid content is decreased, and the flavor is affected thereby. Furthermore, liquid spillage makes the management of the amount of product content difficult, or causes contamination of the production facilities, thus occasionally causing problems in the stable operation of the production and hygiene management.
With regard to plastic containers, it is difficult to perform a seaming process, and there are no plastic containers put in distribution, which are sealed by seaming as in the case of metal can containers for beverage. For plastic containers, the most widely distributed containers are PET (polyethylene terephthalate) bottles. With regard to the PET bottles, a method of screwing a cap on the bottle mouth portion is being used as a sealing method. However, this cap serves as a major cost-increasing factor for the whole container. Additionally, since caps are mainly made of PP (polypropylene), they pose an impediment to recycling.
Even for PET bottles, it has become general to use a high speed production line having a throughput capacity of several hundred bottles per minute. It is general to perform mounting of the lid and sealing using a capper, immediately after filling.
Furthermore, for cup-shaped containers, technologies for heat sealing a lid having a plastic resin layer and an aluminum foil layer by irradiating the lid with laser light, have also been disclosed (see, for example, Japanese Laid-Open Patent Publication No. JP-A-60-193836).